Implantable devices are indicated for an increasing number of patients and an increasing variety of medical conditions. Fully implantable systems are preferred to avoid the need to carry and maintain an external power source, which is inconvenient to the patient and serves as a constant source of worry because the patient is continuously aware of the device. However, fully implantable systems often place design constraints on the power consumption of the device due to the competing objectives of high device longevity versus device compactness.
The use of inductive power coupling of implantable medical devices to help solve this power/size dichotomy is well known. For example, inductive power coupling has been utilized in LVAD (artificial hearts), cochlear implants and respiratory pacemakers.
Inductive power links are of two main types—tightly coupled links versus loosely coupled links. Tightly coupled links are typically characterized by known or close distances between the transmission and reception components. In addition, the geometry of tightly coupled links is typically known or fixed. In contrast, loosely coupled systems operate over variable distances and with unknown or variable geometric orientations. However, loosely coupled systems are typically characterized by low power transmission efficiencies.
Systems to transmit power across a variable coupling distance of 4-8 cm have been demonstrated to attain a transmission efficiency of about 10%. See Benedetti, R. et al., Overview of Telemetry Systems With Inductive Links and Variable Coupling Distances, International Conference on Biotelemetry XIII, March 1995, which is incorporated herein by reference. Systems of this nature have been implemented with transmitter output power from about 100 mW to about 15 Watts. Even if a practical system is limited to 1% efficiency, the amount of power transferable to the implanted device while coupled to the power transmitter can be substantial (relative to the power budget of the typical implanted device). Such inductive power coupling links also have been designed to accommodate two-way or bi-directional communication between the implant and the external device.
Because of the energy/power transfer and communications link capabilities of inductive coupling, it can be used to provide power to multiple devices simultaneously, provide communications with multiple devices simultaneously and provide communications between multiple implantable devices.
A basic example of inductive coupling can be found in U.S. Pat. No. 5,519,262 to Wood. The '262 patent discloses a system for power coupling independent of the position of the receiver over a surface by using a spatially-dependent phase shift in the electromagnetic field generated by the power transmitter. In addition, the '262 patent generally discloses, without specific examples, the potential use of the invention in power and communications transmission. However, the '262 patent does not disclose or claim the use of the technology to power or access data from an implantable medical device.
U.S. Pat. No. 6,083,174 to Brehmeier-Flick et al. discloses an implantable sensor and two telemetry units—one implanted with the sensor within a flexible foil and the other extracorporeal. Although the '174 patent discloses the implanted telemetry unit as being adapted to receive a conductive power transmission from the extracorporeal telemetry unit and to transmit data to that unit, the patent explicitly disclaims the need for an implanted battery. Therefore, the invention described in the '174 patent is incapable of recharging an energy storage device implanted with the medical device. In addition, although the '174 patent describes the use of a personal computer to capture and analyze sensed patient data, it does not disclose the use of a computer network to analyze and correlate sensed patient data from a population of patients.
U.S. Pat. No. 6,240,318 to Phillips discloses a transcutaneous energy transmission system (TETS) to provide power for any kind of implantable device requiring a source of DC power operation. The implantable device may be a mechanical circulatory support system, a left ventricular device, a muscle stimulator, vision prosthesis, audio prosthesis or other implantable device requiring DC electrical power operation. The TETS system is also adapted to recharge an implantable battery. However, the '318 patent is limited to powering devices and is not adapted to communicate patient data to external diagnostic or analytical devices.
U.S. Pat. No. 6,345,203 to Mueller, et al. discloses the use of Magnetic Vector Steering and Half-Cycle Amplitude Modulation to enhance the powering and control of multiple, arbitrarily oriented implant devices. These techniques, according to the patent, enable arbitrarily oriented implants to receive power and command, programming, and control information in a manner that preserves battery life and transmission time while reducing overall implant device bulk. More specifically, the invention of '203 patent is suitable for high-bandwidth (>1 Mbits/sec) biotelemetry that requires large amounts of energy to power the implant. Consequently, the patent suggests alternative or supplemental power sources, such as Inductive Power Transfer. In addition, the preferred use of the invention of the '203 patent is in biomedical implants placed in regions of interest about the heart of a patient. However, the '203 patent does not disclose or claim the use of induction technology to automatically recharge the battery of an implantable medical device and provide intercommunications capability with the device in proximity to an electromagnetic transmission source.
In contrast, U.S. Pat. No. 6,358,281 to Berrang, et al. discloses a cochlear device, which can be implanted, that uses an external, mechanically held, head-mounted device containing an external coil inductively coupled to a receiving coil to periodically recharge the implanted battery of the device. The external and implanted coils also can be used as a communications link to program the implanted electronics of the device. However, the device disclosed in the '281 patent is limited to a cochlear prosthesis and is not for use beyond this limited application. In addition, the inductive coil of the implant is only configured “for receiving” data from an external means. The patent does not disclose uploading data from the implant to an analytical device or network.
Thus, for these and other reasons, there is a need for an automatic system that inductively transmits energy to an implantable medical device to power or recharge the battery of the device and fully communicate with the device or a network of such devices to improve individual patient care or the care of populations of patients. The system further eliminates the need to attach or carry an external device to enable power transmission and intercommunication.